This invention relates to a vent valve for an air braking system of a vehicle.
Vent valves are required in an air braking system in order to drain moisture which may accumulate in the signal or supply lines. Manually operable valves are somewhat difficult to design, and are generally undesirable because they tend to be opened at rather infrequent intervals. Automatic vent valves are therefore preferred, hitherto such automatic valves have included precision engineered components such as pistons, springs and valve seating devices, and are therefore somewhat expensive.
An air braking system of a vehicle also includes a compressor which is brought on-load by a demand signal. When the compressor is off-load, but running, lubrication oil may accumulate on the head of the piston. This oil will enter the air braking system when the compressor is brought on-load, and it has been proposed to vent such oil laden air to exhaust. Again, the vent valve proposed for this purpose is a precision engineered component which is rather expensive.
What is required is an inexpensive and adaptable valve to suit either or both of the aforementioned circumstances.
According to the invention there is provided a vent valve for a fluid pressure circuit, the valve comprising a closed chamber having an inlet port and a vent, the vent defining a valve seat about the inner side thereof and having a resilient valve member engageable with said seat, the valve member comprising a head, a continuous rib depending from said head and adapted for sealing engagement with said seat, and means to hold said valve member adjacent said vent; the rim of said head engaging said chamber about said seat to resiliently support said rib away from said seat, and defining openings whereby said chamber can communicate with said vent; the vent valve thereby defining a fluid passage from said chamber via said openings, seat and vent, and said fluid passage having a restricted flow area such that increasing pressure in said chamber deforms said head towards said vent, thereby sealingly engaging said rib and seat.
Such a valve can be very simply constructed using a unitary moulding of e.g. synthetic rubber. The valve preferably incorporates retaining means to secure the valve member in relation to the vent, these retaining means preferably being provided on the valve member itself. The retaining means may for example be a snap fit projection of the valve member, and in the preferred embodiment comprise a limb removably engageable in the vent itself.
The valve seat and depending rib are preferably circular, the seat being planar and immediately adjacent the vent.
The vent may include a passage having inwardly directed arms defining vent passageways therebetween. The vent may be defined by an annular insert, and such an arrangement permits variation of the area of said vent passageways.
Preferably the depending rib defines with the valve seat a travel stop for the valve member, thereby restricting the stroke of the valve from the rest condition.
The valve is particularly useful in an air braking system of a vehicle, and may be used to vent part of the system automatically. In a preferred embodiment the valve is positioned in the signal line from the governor valve to the compressor, and purges accumulated moisture from this line.